On Fri, Apr 05, 2019 at 01:31:02PM +0200, Vitaly Kuznetsov wrote: > Maya Nakamura <[email protected]> writes: > > > @@ -98,18 +99,20 @@ EXPORT_SYMBOL_GPL(hyperv_pcpu_input_arg); > > u32 hv_max_vp_index; > > EXPORT_SYMBOL_GPL(hv_max_vp_index); > > > > +struct kmem_cache *cachep; > > +EXPORT_SYMBOL_GPL(cachep); > > + > > static int hv_cpu_init(unsigned int cpu) > > { > > u64 msr_vp_index; > > struct hv_vp_assist_page **hvp = &hv_vp_assist_page[smp_processor_id()]; > > void **input_arg; > > - struct page *pg; > > > > input_arg = (void **)this_cpu_ptr(hyperv_pcpu_input_arg); > > - pg = alloc_page(GFP_KERNEL); > > - if (unlikely(!pg)) > > + *input_arg = kmem_cache_alloc(cachep, GFP_KERNEL); > > I'm not sure use of kmem_cache is justified here: pages we allocate are > not cache-line and all these allocations are supposed to persist for the > lifetime of the guest. In case you think that even on x86 it will be > possible to see PAGE_SIZE != HV_HYP_PAGE_SIZE you can use alloc_pages() > instead. > Thank you for your feedback, Vitaly!
Will you please tell me how cache-line relates to kmem_cache? I understand that alloc_pages() would work when PAGE_SIZE <= HV_HYP_PAGE_SIZE, but I think that it would not work if PAGE_SIZE > HV_HYP_PAGE_SIZE. > Also, in case the idea is to generalize stuff, what will happen if > PAGE_SIZE > HV_HYP_PAGE_SIZE? Who will guarantee proper alignment? > > I think we can leave hypercall arguments, vp_assist and similar pages > alone for now: the code is not going to be shared among architectures > anyways. > About the alignment, kmem_cache_create() aligns memory with its third parameter, offset. > > @@ -338,7 +349,10 @@ void __init hyperv_init(void) > > guest_id = generate_guest_id(0, LINUX_VERSION_CODE, 0); > > wrmsrl(HV_X64_MSR_GUEST_OS_ID, guest_id); > > > > - hv_hypercall_pg = __vmalloc(PAGE_SIZE, GFP_KERNEL, PAGE_KERNEL_RX); > > + hv_hypercall_pg = kmem_cache_alloc(cachep, GFP_KERNEL); > > + if (hv_hypercall_pg) > > + set_memory_x((unsigned long)hv_hypercall_pg, 1); > > _RX is not writeable, right? > Yes, you are correct. I should use set_memory_ro() in addition to set_memory_x(). > > @@ -416,6 +431,7 @@ void hyperv_cleanup(void) > > * let hypercall operations fail safely rather than > > * panic the kernel for using invalid hypercall page > > */ > > + kmem_cache_free(cachep, hv_hypercall_pg); > > Please don't do that: hyperv_cleanup() is called on kexec/kdump and > we're trying to do the bare minimum to allow next kernel to boot. Doing > excessive work here will likely lead to consequent problems (we're > already crashing the case it's kdump!). > Thank you for the explanation! I will remove that.
